1. Technical Field
The invention relates to a process for reducing the permeability in a high permeability region of a subterranean hydrocarbon-bearing formation and more particularly to a process for improving conformance in the formation and improving flow profiles of fluids produced from or injected into a wellbore penetrating the hydrocarbon-bearing formation.
2. Description of Related Art
Poor vertical conformance results from the vertical juxtaposition of relatively high permeability geologic zones to relatively low permeability zones within a subterranean formation. Poor areal conformance results from the presence of high permeability streaks and high permeability anomalies within the formation matrix, such as vertical fractures and networks of the same, which have very high permeability relative to the formation matrix. Fluids generally exhibit poor flow profiles and sweep efficiencies in subterranean formations having poor vertical or areal conformance.
Gelation system are commonly injected as sequential slugs into the high permeability regions of a formation exhibiting poor conformance in an effort to improve conformance and flow profiles of fluids therein. U.S. Pat. No. 4,031,958 to Sandiford, et al is typical of such processes wherein the gelation system is sequentially injected into the formation for the purpose of subsequently mixing in situ to form a gel. Sandiford et al and the like are unsatisfactory for the treatment of many formations because mixing and subsequent gelation occur prematurely without fully penetrating the treatment region. Viscosity differences between the sequential gel component slugs of the system promote fingering and rapid mixing of the gel component. Gelation generally occurs at the point of mixing, which can be far ahead of the desired treatment region, especially where the region is a substantial distance from the wellbore. Once the gel forms, it is often unable to penetrate the formation further and permeability reduction is not effected in the desired treatment region.
A process is needed for inhibiting mixing of sequentially injected gel component slugs until the slugs have fully penetrated the desired treatment region. A process is further needed for minimizing premature gelation of a gelation system. A process is needed wherein regions a substantial distance from the wellbore can be treated effectively by a gelation system which gels in situ.